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To keep things manageable, let's use a concrete example Suppose the ELF program that we wish to add to the release code is the since source file hello.c:
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#include <stdio.h>
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int main(int argc, char **argv) { printf("Hello from Add-On Program!\n"); return 0; } |
Let's say that we have a a directory called addon and contains the hello.c source file, a Makefile that will create the the ELF program, and a Bash script called mkdefines.sh that will create the a linker script.
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This is the Makefile that I used to create ELF program:
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include nuttx-export-7.25/build/Make.defs
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# Long calls are need to call from RAM into FLASH
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ARCHCFLAGS += -mlong-calls ARCHWARNINGS = -Wall -Wstrict-prototypes -Wshadow -Wundef ARCHOPTIMIZATION = -Os -fno-strict-aliasing -fno-strength-reduce -fomit-frame-pointer ARCHINCLUDES = -I. -isystem nuttx-export-7.25/include |
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CFLAGS = $(ARCHCFLAGS) $(ARCHWARNINGS) $(ARCHOPTIMIZATION) $(ARCHINCLUDES) -pipe
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CROSSDEV = arm-none-eabi- CC = $(CROSSDEV)gcc LD = $(CROSSDEV)ld STRIP = $(CROSSDEV)strip --strip-unneeded |
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# Setup up linker command line options
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LDRELFLAGS = -r
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LDELFFLAGS = -r -e main LDELFFLAGS += -T defines.ld -T gnu-elf.ld |
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# This might change in a different environment |
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OBJEXT ?= .o
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# This is the generated ELF program
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BIN = hello REL = hello.r |
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# These are the sources files that we use
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SRCS = hello.c OBJS = $(SRCS:.c=$(OBJEXT)) |
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# Build targets
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all: $(BIN) .PHONY: clean |
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$(OBJS): %$(OBJEXT): %.c $(CC) -c $(CFLAGS) -o $@ $< |
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System.map: nuttx-export-7.25/System.map cat nuttx-export-7.25/System.map | sed -e "s/\r//g" >System.map |
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$(REL): $(OBJS) $(LD) $(LDRELFLAGS) -o $@ $< |
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defines.ld: System.map $(REL) ./mkdefines.sh System.map "$(REL)" >defines.ld |
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$(BIN): defines.ld $(REL) $(LD) $(LDELFFLAGS) -o $@ $(REL) $(STRIP) $(REL) |
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clean: rm -f $(BIN) rm -f $(REL) rm -f defines.ld rm -f System.map rm -f *.o |
The Linker Script
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The main linker script that I am using in this example, gnu-elf.ld, contains the following:
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SECTIONS { .text 0x00000000 : { _stext = . ; *(.text) |
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*(.text.*) |
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*(.gnu.warning) |
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*(.stub) |
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*(.glue_7) |
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*(.glue_7t) |
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*(.jcr) |
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_etext = . ; } |
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.rodata : { _srodata = . ; *(.rodata) |
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*(.rodata1) |
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*(.rodata.*) |
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*(.gnu.linkonce.r*) |
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_erodata = . ; } |
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.data : { _sdata = . ; |
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*(.data) *(.data1) |
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*(.data.*) |
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*(.gnu.linkonce.d*) |
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_edata = . ; } |
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.bss : { _sbss = . ; *(.bss) |
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*(.bss |
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.*) *(.sbss) |
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*(.sbss.*) |
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*(.gnu.linkonce.b*) |
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*(COMMON) |
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_ebss = . ; } |
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/* Stabs debugging sections. */ |
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.stab 0 : { *(.stab) } .stabstr 0 : { *(.stabstr) } .stab.excl 0 : { *(.stab.excl) } .stab.exclstr 0 : { *(.stab.exclstr) } .stab.index 0 : { *(.stab.index) } .stab.indexstr 0 : { *(.stab.indexstr) } .comment 0 : { *(.comment) } .debug_abbrev 0 : { *(.debug_abbrev) } .debug_info 0 : { *(.debug_info) } .debug_line 0 : { *(.debug_line) } .debug_pubnames 0 : { *(.debug_pubnames) } .debug_aranges 0 : { *(.debug_aranges) } } |
Creating the defined.ld Linker Script
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Here is the version of mkdefines.sh that I used in this demo:
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#!/bin/bash
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usage="Usage: $0 <system-map> <relprog>"
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# Check for the required path to the System.map file
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sysmap=$1 if [ -z "$sysmap" ]; then echo "ERROR: Missing <system-map>" echo "" echo $usage exit 1 fi |
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# Check for the required partially linked file
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relprog=$2 if [ -z "$relprog" ]; then echo "ERROR: Missing <program-list>" echo "" echo $usage exit 1 fi |
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# Verify the System.map and the partially linked file
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if [ ! -r "$sysmap" ]; then echo "ERROR: $sysmap does not exist" echo "" echo $usage exit 1 fi |
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if [ ! -r "$relprog" ]; then echo "ERROR: $relprog does not exist" echo "" echo $usage exit 1 fi |
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# Extract all of the undefined symbols from the partially linked file and create a # list of sorted, unique undefined variable names. |
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varlist=`nm $relprog | fgrep ' U ' | sed -e "s/^[ ]*//g" | cut -d' ' -f2 | sort - | uniq`
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# Now output the linker script that provides a value for all of the undefined symbols
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for var in $varlist; do map=`grep " ${var}$" ${sysmap}` if [ -z "$map" ]; then echo "ERROR: Variable $var not found in $sysmap" echo "" echo $usage exit 1 fi |
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varaddr=`echo ${map} | cut -d' ' -f1` echo "${var} = 0x${varaddr} | 0x00000001;" done |
This script basically just uses the nm utility to find all of the undefined symbols in the ELF object. Then it searches for the address of each undefined symbol in the System.map that was created when the released firmware was created. Finally, it uses the symbol name and the symbol address to create each symbol table entry.
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